Preparation and spinning of nitric acid polyacrylonitrile solutions



United States Patent 3,410,941 PREPARATION AND SPINNING 0F NITRIC AClDPOLYACRYLUNITRILE SOLUTIONS Roland Dagon and Camille Nordmann, Fribourg,Switzerland, assignors to Lonza Ltd, Gampel, Valais, Switzerland,direction: Basel, Switzerland No Drawing. Continuation-impart ofabandoned applications Ser. No. 258,960, Feb. 14, 1963, and Ser. No.402,615, Oct. 8, 1964. This application Mar. 30, 1967, Ser. No. 626,936

Claims priority, application Switzerland, Feb. 16, 1962, 1,952/62; Oct.9, 1963, 12,393/63 9 Claims. (Cl. 264-482) ABSTRACT OF THE DISCLOSUREAcrylonitrile is polymerized in a concentrated nitric acid, and thepolymer solution is spun into a nitric acid bath of lower concentration.The nitric acid of the spinning bath may be recovered and reused assolvent for the monomer.

This application is a continuation-in-part of our applications Ser. No.258,960, filed Feb. 14, 1963, and 402,- 615, filed Oct. 8, 1964, bothnow abandoned.

This invention relates to the preparation and spinning of syntheticfibers from nitric solutions of polymers and copolymers ofpolyacrylonitrile.

It is known to prepare spinnable polyacrylonitrile solutions bydissolving the polyacrylonitrile in concentrated nitric acid. In theindustrial utilization of such nitric acid solutions ofpolyacrylonitrile, as they are disclosed in Patent No. 2,878,097 andparticularly in Patent No. 2,928,715, a serious drawback developed. Thesolutions contained always jelly-like inclusions which in spinningproduced acclusions of the spinnerets; as a result the carrying out ofthe process was rendered more difiicult and the obtained fibers were notof uniform quality. In order to remove the inclusions, filtrationsthrough high pressure filters was necessary, which are of high runningand maintenance cost and therefore constitute a serious economicdraw-back.

Said jelly-like inclusions are believed to be polymer agglomerationswhich are not properly dissolved but only swollen. Attempts to avoidformation of such gel inclusions by using higher concentrated acids orhigher temperatures were not successful and produced other drawbacks.

We have found the formation of obnoxious persistent jelly-likeinclusions is prevented and that the filtration of the nitric acidpolyacrylonitrile solutions for spinning can be avoided when thepolyacrylonitrile is preformed by polymerizing the monomer in theconcentrated nitric acid itself.

Former investigators in the polyacrylonitrile art had, from the start,discarded any idea of contacting also monomeric acrylonitrile withconcentrated nitric acid because of the well known differences in thechemical behavior of the monomer and polymer. Whilst polyacrylonitrilewas known to be very resistant to strong inorganic acids under specificconditions as pointed out in patent specification 2,928,715 due to theclose packing of adjacent chains which protects the otherwise veryreactive nitrile groups and is considered responsible for the quiteunique properties of the polymer, it was also well known that themonomer is extremely reactive. The monomer has two readily accessiblereactive groups, the double bond and the nitrile group. In contrast tothe polymer, where the nitrile groups are believed to be so close as toenter some form of strong linkage with each other, the nitrile group inthe monomer has still its normal activity. The double bond is known toattach readily water under the catalytic influence of acids, includingnitric acid (see eg G. M. Schwab, Handbook of catalysis, vol. VI, 2ndpart, p. 37), and the nitrile group in monomeric nitriles is easilysaponified by treatment with concentrated nitric acidv (e.g. Ger. PatentNo. 627,029).

Under these circumstances, the discovery that acrylonitrile monomercould be kept unattacked in concentrated nitric acid solution for a timesufiicient to achieve polymerization, came as a complete surprise.

It has been known to polymerize acrylonitrile in dilute nitric acidwhere the N0 ions were used in coaction with oxalate ions to act aspolymerization catalysts. In said known process, very low nitric acidconcentrations were used so that water, and not the nitric acid, actedas solvent for the monomeric acrylonitrile, whereby the polymer, whenformed, precipitated and did not remain in solution.

According to the invention, acrylonitrile is polymerized in nitric acidof a concentration sulficient to maintain the polymer in solutions underconditions where no gel inclusions are formed in the polymer and wherethe monomer is substantially not decomposed or hydrolyzed. Saidconditions require that the acrylonitrile is dissolved in an aqueousnitric acid containing 50* to percent, preferably 50 to 68 percent, byweight of HNO to a solution which contains preferably 5 to 30 percent byWeight of the monomer whereby the temperature of the solution ismaintained below 20 C., preferably in the range of 15 to +15 C.

The acrylonitrile polymer can be obtained either by homopolymerizationor by copolymerization with other polymerizable ethylenicallyunsaturated compounds, whereby however, the polymer should contain atleast percent by weight of acrylonitrile units. Such copolymerizablecompounds are, for example, vinyl compounds whose stability is notsubstantially interior with respect to the polymerisation medium than.acrylonitrile itself, such as vinyl pyridine, vinyl esters, styrene ormethylstyrene, N-vinylsuccinimide, acrylic, methacrylic and itaconicacid and their derivatives or homologues such as their esters, amides,etc; unsaturated sulfonic acids such as vinyl, allyl, methallyl, styrenesulfonic acid and their salts; unsaturated nitriles such asmethacrylonitrile or vinylidene cyanide.

The monomer is introduced into the solvent in amounts of up to 30preferably from 10 to 30 percent by weight, calculated on the solvent.

Nitric acid of an HNO content of 50 to 75% by weight is an excellentsolvent of acrylonitrile, as shown in the following table giving thesolu-bilities of acrylonitrile at 3 and 18 C.

Percent acrylonitrile in saturated The stability of the acrylonitrile,dissolved in aqueous nitric acid of 5075 HNO content is remarkable andunexpected. Even after prolonged standing, for instance for 152 hours at3 C. or for 48 hours at room temperature, neither addition of water tothe double bond nor nitration of oxidation could be observed.

Also the stability of the nitrile groups of the acrylonitrile in nitricacid of the recited concentrations is surpn'singly good. No hydrolysisof the nitrile group can be observed in 60% nitric acid at roomtemperature of at 3 C. after 24 hours or 48 hours standing,respectively.

The process of the invention consists essentially in dissolvingmonomeric arcrylonitrile in aqueous nitric acid containing 50 to 75,preferably 54 to 68 percent, by weight of HNO and polymerizing theacrylonitrile in said solution in the presence of a catalyst. Generally,temperatures below 30 C., preferably between 20 and 10 C. or -l C. haveto be used if polymers having undegraded nitrile groups are to beproduced. The temperature has greater influence on the hydrolyticdegradation of the nitrile groups than the HNO concentration in thesolvent.

The above general description will allow to adjust readily the operatingconditions for each case by a few preliminary tests, whereby also theshelf life of the polymer solution prior to its application must betaken into account for time calcutions. For short times, for instancefor 1 to 2 hours, the polymerization temperature in 60% nitric acid maybe higher, for instance 30 to 50 C. without causing any hydrolysiseffects in the monomer or polymer. However, as soon as thepolymerization is terminated at such operating temperatures, the systemmust be cooled very quickly, preferably to temperatures below C. becausestanding or storage of the formed polymer solution at said highertemperatures would quickly result in a product having hydrolyzed nitrilegroups.

Although polymerization takes already place in nitric acid having an HNOcontent as said above, the polymerization must be carried out inpresence of a suitable catalyst or catalyst system.

Numerous polymerization accelerators are available to adjust the rate ofpolymerization. Suitable catalysts are organic and inorganicazocompounds, such as 2,2'-azodi- (isobutyronitrile), 2,2'-azodi(2,4-dimethylvaleronitrile), azodisulfonic acid; per acids such asperacetic acid, perbenzoic acid, peroxymonosulfuric acid (Caros acid),peroxydisulfuric acid, peroxynitric acid; organic peroxides, such asbenzoyl peroxide, acetyl peroxide; perborates, and the like.

Catalytically acting redox systems may be formed by adding to the nitricacid solvent or to the recited oxidizing compounds small amounts ofreadily oxidizable substances, such as alkali metal bisulfites; sulfinicacids, such as formamidinsulfinic acid, benzenesulfinic acid; ascorbicacid; and similar compounds.

Traces of certain metals such as iron, copper, titanium, silver, have anactivating effect on the polymerization accelerators. The metals areused in an amount which does not exceed 1% of the monomer involved. Themechanism of this activation is not exactly known as said metals alonehave no catalytic action on the polymerization.

The rate of polymerization may also be influenced by UV-irridiation.UV-irridiation may however also be used in addition to the abovementioned polymerization accelerators or accelerating systems.

According to a preferred embodiment of the invention, the polymerizationis carried out in the presence of a cat alyst system consisting of aperoxydic compound and a metal dicarbonyle compound.

Suitable peroxidic compounds are, for instance, peroxydisulfuric acidand its alkali metal salts, peroxymonosulfuric acid (Caros acid). Theyare employed preferably in amounts of 0.0001 to 0.02 mole per mole ofmonomer.

The metal component of the metallic dicarbonyl compound may be forinstance copper, iron, silver, vanadium or uranium, the two latters intheir vanadyle or uranyle form.

The dicarbonyl component of the metal dicarbonyl compounds may be anorganic compound containing at least two carbonyl groups one of which iscapable to pass into the enol form: such compounds are, for instance,acetoacetic esters such as methylacetoacetate, acetyl acetone, benzoylacetone, acetoacetanilide, dibenzoyl methane, barbituric acid,resorcinol, phloroglucinol.

The metal dicarbonyl compound may be added as Such to the reactionmixture or may be formed in situ. We assume that the metal dicarbonylcompound acts as an activator as its addition shortens the initiationperiod of the polymerization. In addition, it is possible to influencethe course of the polymerization reaction and the molecular weight ofthe formed polymer by means of the metal dicarbonyl compound,particularly by using an excess of the metal or dicarbonyl componentwhen the compound is prepared in situ. It is of advantage to use 0.00001to 0.02 mole of metal dicarbonyl compound per mole of monomer. In thepreferred in situ formation of the metal dicarbonyl compounds, weintroduce 0.00001 to 0.02 mole of dicarbonyl compound and 0.00001 to0.02 equivalent gram of metal salt per mole of monomer, capable to formthe metaldicarbonyl compound such as those comprised in a group formedby copper-, iron-, silvcr, nitrate, sulfate, borate, carbonate,phosphate, arsenate.

Generally, the polymerization is carried out in a closed vessel which isequipped with stirring means and cooling and heating means. It is ofadvantage to sweep prior to the reaction the reaction space with aninert. gas. The reaction can be carried out continuously or as a batchprocess at normal, superatmospheric or reduced pressure. Preferably, themonomers are introduced in such amounts that the obtained polymersolution can be directly used or spun to filaments. As a rule, theamount of monomer will be so adjusted as to produce a solutioncontaining 10 to percent by weight of polymer. The reaction may bestarted with the total required amount of monomer, or only a portion maybe introduced at the start and the balance may be progressively added.The polymer concentration in the solution can also be set by addingnitric acid during the polymerization so as to have at the end of thepolymerization a solution whose polymer content is for example 15% ifthe monomer concentration in the polymerization solution is higher than15%.

It is of particular advantage to carry out the process of the inventionso as to allow the copolymerization in presence of nitric acid oftemperature sensitive monomers such as unsaturated aliphatic or aromaticsulfonic acids, which improve the dyeability of the obtained fibers.

During the polymerization, the concentration of the nitric acid may beadjusted by addition of stronger or weaker acid.

If nitrogen oxides are present or developed during the processing, theymay be removed by degassing under reduced pressure or by addition ofsmall amounts of urea.

Otherwise included gases, for example those included during thepolymerization such as nitrogen or air or any other gas can readily beremoved during the above or separate subsequent degassing steps. Suchdegassing must take place at the latest before the spinneret, preferablybefore the spinning pump.

The reaction is carried out to obtain polymers with unmodified nitrilegroups, which polymers are free of gellike swollen inclusions. The termsolution when used herein is not used in the pure physical sense asdefining a composition Where each molecule is surrounded by the solventand therefore, all individual molecules of the solid are separated fromeach other. We use the term solution in its conventional technical senseto bring out that the acrylonitrile polymer is present in a homogeneousliquid phase suitable for spinning, from which it can be regenerated.

The following examples are given to illustrate but not to limit theinvention.

EXAMPLE 1 A reaction vessel of 250 cc., a glass container equipped withstirrer and cooling means was used. The container was filled with thefollowing batch: 113 g. HNO x g. Fe(NO -9H O, y g. KHSO and z g.ammonium peroxydisulfate.

Polymer Number of yield alter hydrolyzed x y z 96 hours k-valuc nitrilegroups (percent) (percent) 2 0 45 84. 7 Abt. 0.1 0 3 0 57 74.3 Abt. 0.10.03 2 0 68 85. 0 Abt. 01 0.03 2 1 72 80. AM. 0. 1

EXAMPLE 2 Into an enameled agitating vessel, there were introduced: 225g. acrylonitrile; 1275 g. 60% HNOg; 4.5 g. ammonium peroxydisulfate;0.675 g. ascorbic acid; 0.200 g. iron powder.

The polymerization was carried out for 3 hours at 22 C. and for 4additional hours at about C. The thus for-med viscous solution wasprecipitated in water and 182 g. of polymer corresponding to a yield of81% were obtained. No substantial hydrolytic degradation of the nitrilegroups could be observed.

EXAMPLE 3 Into an apparatus as used in Example 2, there were introduced75 g. of acrylonitrile and 425 g. of 60% HNO The air was displaced bynitrogen, and every minutes for 90 minutes there were added at 15 C.with stirring 2 ml. of a 10% aqueous monopersulfuric acid solution and0.1 g. of ascorbic acid. Subsequently, there were added still twice 0.1g. of ascorbic acid each at intervals of 1 hour.

After a total of 24 hours stirring at 15 C., the viscous solution wasprecipitated as described in Example 1. There were obtained 71.3 g. ofpolymer, corresponding to a yield of 95%. Substantially no hydrolysiscould be observed at the polymer molecule.

EXAMPLE 4 This test was made under the same conditions as described inExample 3 but using 75 g. of a monomer mixture consisting of: 68.6 g.acrylonitrile; 6.0 methyl-acrylate; 0.4 g. sodium :rnethallylsulfonate.

After 24 hours of polymerization, the obtained solution cooled to 0 C.,and 0.5 cm. of acetylacetone were added.

The reaction mixture was slowly stirred for 18 hours at a reactiontemperature in the range of O to 2 C.: gradually, a highly viscousspinnable solution was formed which finally contained 73.5 g. ofpolymer, corresponding to a yield of 98%. The polymer had a k-value(according to Fikentsc'her) of 78.9. The IR spectrogram showed that atleast 99.5 percent of the nitrile groups had been retained in thepolymer molecule.

EXAMPLE 6 Under the same conditions as set forth in Example 5, 69 g. ofacrylonitrile and 6 g. of methyl acrylate were copolymerized. Theobtained polymer solution contained 72 g. of copolymer, corresponding toa yield of 96%. The IR-spectrum showed that about 8% of methyl acrylateis incorporated in the copolymer and that at least 99.5 percent of thenitrile groups have remained unchanged, i.e. were not hydrolyzed.

EXAMPLE 7 A stainless steel vessel cooled with brine at 0 C. andequipped with a blade agitator was carefully purged with nitrogen andcharged, with stirring, with 118.330 kg. nitric acid (medium), 19,108kg. acrylonitrile (comonomer), 1.670 kg. methyl acrylate (comonomer),0.104 kg. sodium methallyl sulfonate (comonomer), 0.840 kg. ammoniumpersulfate (amnioniumperoxydisulfate), 0.020 kg. Fe(NO .9H O.

140 cm. of acetylacetone were added to the reaction mixture cooled to 0C. After a reaction time of 22 hours at about 0 C., a spinnable polymersolution was obtained. The polymer yield was 99%; the k-value of thepolymer was 71.5. The solution could be spun, for instance, according tothe method disclosed in US. Patent No. 2,878,097.

The thus obtained filaments presented good physical properties andexcellent dyeability with eg. basic dyestuffs. The IR spectrum showedthat more than 99.5 percent of the original nitrile groups had remainedunchanged in the polymer.

EXAMPLE 8 As described in Example 5, there were polymerized 75 g. ofacrylonitrile in 425 g. of 60% nitric acid containing 3 g. of ammoniumperoxydisulfate, a metal salt, and a compound containing at least 2carbonyl groups.

The following table lists the metal salts, the compound containing atleast 2 carbonyl groups, the amounts employed, the yields, and thek-values (Fikentscher) after a reaction time of 22 hours.

TABLE Number Metal Salt Compound containing at least 2 carbonyl Yield,1:

groups Percent .05 g. C11(N03)2-3H2O 0.5 g. Acetylacetone 97 81. 3 .075g. Fe(NO -9I I2O 2.0 g. Acetoacetanilide 96 84. 2 .075 g. Fe(NO 9H2O 1.0g. Dibenzoyl methane 96 80.5 .075 g. Fe(N 093-91120 2.8 g.5,5-dimethyl-1,3-cyclohexandione. 99 90. 4 .075 g. Fe(NOa)3'9 H2O 1.0 g.Barbiturio acid 100 92. 5 .075 g. Fe(NO -9H2O. 0.5 g. Phloroglucinol 9973.8 .3 g. Iron acetylacetonate 99 79. 3

was precipitated as described in Example 1 and 66 g. of polymer wereobtained, corresponding to a yield of 88 percent, calculated on themonomer. The polymer contains approximately 90% acrylonitrile groups.Substantially no hydrolysis of the nitrile groups in the polymer couldbe observed.

EXAMPLE 5 A three-neck flask equipped with stirrer and thermometer waspurged with nitrogen and cooled by an ice water bath; it was chargedwith 425 g. of 60% nitric acid, 75 g. of acrylonitrile, 3g. of ammoniumperoxydisulfate, and

place.

The IR spectra of the polymers showed that substantially nosaponification of the nitrile groups had taken EXAMPLE 9 0.075 g. ofFe(NO -9H O, said reaction medium was no nitrile groups had beensaponified in the polymer.

7 EXAMPLE 10 A mixture of 72 g. of acrylonitrile and 3 g. ofdimethylaminoethylmethacrylate were polymerized as shown in Example 5.The polymer obtained with a yield of 98% had a k-value of 75.6. Fibersmade from this polymer showed excellent dyeability with e.g. acidicdyestuffs.

EXAMPLE 1 l A spinning solution of 15% polymer content produced as inExample 7 was degassed in vacuo and extruded through a spinneret of 3000holes having a hole diameter of 0.12 mm., at a speed of 10 m./min. intoa spinning bath having an HNO concentration of 36% after a residencelength of 2000 millimeters. The tow was drawn at a speed of 5 m./min. onthe first drawing device, then washed free of nitric acid on a drum,stretched to 800% of its original length in a hot water bath, steamedand shrunk. A yarn of 5 den. per filament in which less than 0.1% of thenitrile groups were saponified, showing a low tendency of pilling, wasobtained.

In all examples, the spinning solution was homogeneous and free ofstreaks of jelly-like swollen inclusions.

The solution obtained according to the invention is ready for spinningand need not be ripened, although such ripening is not harmful to thesolution provided that the temperature and the duration do not alteratethe dissolved polymer. This would occur if such temperature was too highand the time too long. Generally speaking, it is safe to remain with thetemperature below 3 C. preferably between 0 and l5 C. while the timeshould not exceed 72 hours at the lower temperatures.

After degassing and, if necessary, filtration to eliminate foreignmatters, the solution is passed through a spinning pump to thespinnerets and is spun in an aqueous spinning bath. This aqueousspinning bath consists of nitric acid with an HNO concentration of 0 to46% preferably 20 to 44%. The spinning bath temperature lies preferablybetween and 10 C. The spinning can be done with a negative or positivestretch on the first drawing device, according to the desired titer ofyarns.

In addition to providing a simple and uniform economic procedure for theproduction of polyacrylonitrile fibers directly from the monomer, theprocess of this invention has the further advantage to use a singlesolvent, aqueous nitric acid, for the solution of the monomer, for thepolymerization of the monomer, for the solution of the polymer, and asspinning bath for precipitating the filaments from the polymer solution.Therefore, if the concentration of the nitric acid in the spinning bathhas become too high, said nitric acid, if necessary after furtherconcentration, can be used as solvent for the monomer; thus, the nitricacid required for the process can be recycled.

We claim:

1. A process for the preparation of spinnable solutions of acrylonitrilepolymers containing at least 80 percent of acrylonitrile units, thebalance being ethylenically unsaturated compounds copolymerizable withacrylonitrile, said process comprising dissolving acrylonitrile monomerin concentrated aqueous nitric acid containing 50 to 75 percent byweight of HNO at a temperature in the range of to +30 to a solutioncontaining up to 30 percent by weight of said monomer, and polymerizingsaid monomer in said solution in the presence of a polymerizationcatalyst.

2. The process as claimed in claim 1 wherein the concentrated nitricacid has an HNO content of 54 to 68%.

3. The process as claimed in claim 1 wherein said catalyst is a peroxidecompound in an amount of 0.0001 to 0.02 moles per mole of monomer.

4. The process as claimed in claim 1 wherein said catalyst is presenttogether with 0.00001 to 0.02 moles, per mole of monomer, of a metaldicarbonyl compound of a metal selected from the group consisting ofcopper, iron and silver.

5. The process as claimed in claim 1 wherein the dicarbonyl compound isformed in situ whereby 0.00001 to 0.02 moles of dicarbonyl compound and0.00001 to 0.02 equivalent grams of a salt comprised in the groupconsisting of copper iron-, silver nitrate, sulfate, borate, carbonate,phosphate, arsenate are employed.

6. An aqueous solution having a temperature of 15 to 15 C. containing 50to nitric acid and dissolved therein 10 to 30 percent by weight ofmonomeric acrylonitrile, said solution being stable for a period of timesufficient to allow shipping thereof from a monomer production stationto a polymerization station.

7. A process for producing polyacrylonitrile fibers containing at leastpercent of acrylonitrile units, the balance being ethylenicallyunsaturated compounds copolymerizable with acrylonitrile, said processcomprising dissolving acrylonitrile monomer in concentrated aqueousnitric acid containing 54 to 68 percent by weight of HNO at atemperature in the range of l5 to +30 C. to a solution 10 to 30 percentby weight of said monomer, polymerizing said monomer in said solution inthe presence of a polymerization catalyst, passing said polymer solutionthrough a spinneret into a spinning bath containing 20- to 46 percent byweight of HNO maintaining the temperature of said spinning bath in therange of +10 to 10 C., thereby forming fibers and washing, stretchingand drying said fibers.

8. A process as claimed in claim 7 wherein said catalyst is an inorganicperoxidic compound in an amount of 0.0001 to 0.02 moles per mole ofmonomer together with 0.0001 to 0.02 moles per mole of monomer of anmetal dicarbonyl compound of a metal selected from the group consistingof copper, iron and silver.

9. A process as claimed in claim 7 wherein the HNO concentration of thespinning bath is maintained at its level by adding washing water, andtaking the overflow to a distilling step distilling said overflow andrecovering nitric acid with an HNO content of 50 to 68% by weight.

References Cited UNITED STATES PATENTS 2,612,490 9/1952 Gould 26088.7 X3,073,669 1/1963 Fujisaki et al. 264206 X 3,080,209 3/1963 Fujisaki etal 264-206 X 3,147,322 9/1964 Fujisaki et al. 264182 3,202,641 8/1965Nakajima et al 260-29.6 3,287,304 11/1966 Fujisaki et al 260-29.6

FOREIGN PATENTS 628,520 8/1963 Belgium. 3,511,687 8/1960 Japan.

JAMES A. SEIDLECK, Primary Examiner.

J. H. WOO, Assistant Examiner.

